Hyperprolactinemia in acute myeloid leukemia and indication of ectopic expression of human prolactin in blast cells of a patient of subtype M4

Prolactin receptor signaling induces acquisition of chemoresistance and reduces clonogenicity in acute myeloid leukemia

BACKGROUND

Development of precision medicine requires the identification of easily detectable and druggable biomarkers. Despite recent targeted drug approvals, prognosis of acute myeloid leukemia (AML) patients needs to be greatly improved, as relapse and refractory disease are still difficult to manage. Thus, new therapeutic approaches are needed. Based on in silico-generated preliminary data and the literature, the role of the prolactin (PRL)-mediated signaling was interrogated in AML.

METHODS

Protein expression and cell viability were determined by flow cytometry. Repopulation capacity was studied in murine xenotransplantation assays. Gene expression was measured by qPCR and luciferase-reporters. SA-β-Gal staining was used as a senescence marker.

RESULTS

The prolactin receptor (PRLR) was upregulated in AML cells, as compared to their healthy counterpart. The genetic and molecular inhibition of this receptor reduced the colony-forming potential. Disruption of the PRLR signaling, either using a mutant PRL or a dominant-negative isoform of PRLR, reduced the leukemia burden in vivo, in xenotransplantation assays. The expression levels of PRLR directly correlated with resistance to cytarabine. Indeed, acquired cytarabine resistance was accompanied with the induction of PRLR surface expression. The signaling associated to PRLR in AML was mainly mediated by Stat5, in contrast to the residual function of Stat3. In concordance, Stat5 mRNA was significantly overexpressed at mRNA levels in relapse AML samples. A senescence-like phenotype, measured by SA-β-gal staining, was induced upon enforced expression of PRLR in AML cells, partially dependent on ATR. Similar to the previously described chemoresistance-induced senescence in AML, no cell cycle arrest was observed. Additionally, the therapeutic potential of PRLR in AML was genetically validated.

CONCLUSIONS

These results support the role of PRLR as a therapeutic target for AML and the further development of drug discovery programs searching for specific PRLR inhibitors.

Domperidone use and risk of primary liver cancer in the Clinical Practice Research Datalink

BACKGROUND

Pronounced sex-disparity in liver cancer suggests a role for hormones, one of which could be prolactin. Stimulation of prolactin production in mice via domperidone has been reported to decrease hepatocarcinogenesis, thus may have chemopreventive potential. To study the effect of domperidone in humans, a large medical records study was conducted.

METHODS

Based in the Clinical Practice Research Datalink, 1921 liver cancer cases and 7681 controls were identified. Conditional logistic regression was employed to estimate odds ratios (OR) and 95% confidence intervals (CI). Domperidone use was analyzed overall, and by number of prescriptions and cumulative dose.

RESULTS

Comparing ever- versus never-use, there was no association between domperidone and liver cancer among men (OR = 1.06, 95% CI: 0.76-1.48) or women (OR = 1.21, 95% CI: 0.82-1.76). Among men, there was no association with dose or number of prescriptions, while among women who received the highest doses (OR_{2700 mg vs. 0 mg} = 2.52, 95% CI: 1.18-5.41, p-trend = 0.02) and greatest number of prescriptions (OR_{≥11 Rx vs. 0 Rx} = 3.17, 95% CI: 1.07-9.40, p-trend = 0.02) there was a significantly increased risk, although there was no evidence of heterogeneity in the results by gender.

CONCLUSION

Domperidone use was not associated with decreased liver cancer risk among all study participants. Among women, an increased risk at highest levels of exposure warrants further study.

Paraneoplastic Galactorrhea in Childhood T-ALL: An Evaluation of Tumor-derived Prolactin

T-cell acute lymphoblastic leukemia (T-ALL) comprises 15% of childhood leukemia. Although multiagent pulse chemotherapy has improved event-free survival in recent decades, the lack of reliable prognosticators and high rate of relapse remain a challenge. Described is a novel discovery of tumor-derived hyperprolactinemia in childhood T-ALL through a case associated with paraneoplastic galactorrhea. Prolactin production by tumor cells, although a rare phenomenon, is previously demonstrated in several adult cancers and 2 pediatric malignancies with unknown implications. This is the first report demonstrating tumor-derived prolactin in pediatric T-ALL and offers potential as a disease marker and therapeutic drug target.

Novel evidence that pituitary gonadotropins directly stimulate human leukemic cells-studies of myeloid cell lines and primary patient AML and CML cells

We recently reported that normal hematopoietic stem cells express functional pituitary sex hormone (SexH) receptors. Here we report for the first time that pituitary-secreted gonadotrophins stimulate migration, adhesion, and proliferation of several human myeloid and lymphoid leukemia cell lines. Similar effects were observed after stimulation of human leukemic cell lines by gonadal SexHs. This effect seems to be direct, as the SexH receptors expressed by leukemic cells responded to stimulation by phosphorylation of MAPK_p42/44 and AKT_ser473. Furthermore, in parallel studies we confirmed that human primary patient-derived AML and CML blasts also express several functional SexH receptors. These results shed more light on the potential role of SexHs in leukemogenesis and, in addition, provide further evidence suggesting a developmental link between hematopoiesis and the germline.

Acute myeloid leukemia presenting as galactorrhea

Acute myeloid leukemia (AML) presents with symptoms related to pancytopenia (weakness, infections, bleeding diathesis) and organ infiltration with leukemic cells. Galactorrhea is an uncommon manifestation of AML. We report a case of AML presenting with galactorrhea.

Pineal Diffuse Large B-Cell Lymphoma Concomitant With Pituitary Prolactinoma: Possible Correlation Between 2 Distinguished Pathologies: A Case Report

This is the first reported case of pineal lymphoma with concomitant prolactin-producing pituitary adenoma.A 51-year-old male experienced worsening headaches accompanied by nausea, diplopia, and memory loss for 1 month. Cranial nerve examination revealed bilateral upward gaze limitation with convergence impairment, which is known as Parinaud syndrome. Magnetic resonance images revealed a mass in the pineal gland with a coexisting mass within the enlarged sella fossa. Hormone analysis revealed hyperprolactinemia. The pineal mass was removed without injuring the hypothalamus, brain stem, or any neighboring vessels. Pathology examination confirmed the diagnosis of diffuse large B-cell lymphoma (DLBCL) involving the pineal gland. After further studies, the pineal lymphoma was determined to be a secondary tumor from a gastric primary tumor. The patient died 6 months after diagnosis due to systemic progression of DLBCL.Although the mechanistic link between hyperprolactinemia and lymphoma progression has not been clarified on a clinical basis, high prolactin levels may contribute to the rapid progression and therapeutic resistance of the lymphoma.

Increased micronucleus, nucleoplasmic bridge, nuclear bud frequency and oxidative DNA damage associated with prolactin levels and pituitary adenoma diameters in patients with prolactinoma

Prolactinoma is the most common pituitary tumor. Most pituitary tumors are benign, but they often are clinically significant. We investigated cytokinesis-block micronucleus cytome (CBMN cyt) assay parameters and oxidative DNA damage in patients with prolactinoma to assess the relations among age, prolactin level, pituitary adenoma diameter and 8-hydroxy-2'-deoxyguanosine (8-OHdG) level in patients with prolactinoma. We investigated 27 patients diagnosed with prolactinoma and 20 age- and sex-matched healthy controls. We measured CBMN cyt parameters and plasma 8-OHdG levels in peripheral blood lymphocytes of patients with prolactinoma and controls. The frequencies of micronucleus (MN), nucleoplasmic bridge, nuclear bud, apoptotic and necrotic cells, and plasma 8-OHdG levels in patients with prolactinoma were significantly greater than controls. MN frequency was correlated positively with age, prolactin levels and pituitary adenoma diameters in patients with prolactinoma. The increased chromosomal and oxidative DNA damage, and the positive correlation between MN frequency, prolactin levels and pituitary adenoma diameters may be associated with increased risk of cancer in patients with prolactinoma, because increased MN frequency is a predictor of cancer risk.

Acute lymphoblastic leukaemia presenting with galactorrhoea

A teenage girl presented with galactorrhoea and moderate hyperprolactinaemia. She was subsequently diagnosed to have acute lymphoblastic leukaemia. Further investigations supported the presence of ectopic prolactin production as suggested by the presence of prolactin mRNA in the patient's marrow at diagnosis. Both the ectopic prolactin mRNA and galactorrhoea eventually resolved upon disease remission after treatment.

Cancer risk in hyperprolactinemia patients: a population-based cohort study

OBJECTIVE

Experimental evidence indicates that prolactin might play a role in tumorigenesis of several human cancers, but data on cancer risk in hyperprolactinemia patients are sparse. The aim of this study was to investigate cancer risk in hyperprolactinemia patients. Design A population-based matched cohort study in Sweden.

METHODS

The hyperprolactinemia cohort consisted of patients hospitalized for hyperprolactinemia from 1987 to 1995 identified in the National Patient Register (n=585) and a hospital cohort of prolactinoma patients at Karolinska University Hospital (n=384). For each patient, ten matched individuals were identified via the Register of Population. Cancer occurrence was ascertained via the Swedish Cancer Registry. Hazard ratios (HRs) were estimated by Cox proportional hazards regression.

RESULTS

Seventy-three malignant tumors were identified in the hyperprolactinemia patients and 660 tumors in the comparison group (HR 1.31; 95% confidence interval (CI): 1.02-1.68), mainly attributed to an increased risk of upper gastrointestinal cancer in both males and females (HR 3.69; 95% CI: 1.70-8.03) and hematopoietic cancer in females (HR 3.51; 95% CI: 1.06-11.6). Twelve breast cancers occurred in the female patients, corresponding to an HR of 1.09 (95% CI: 0.60-1.99). Prostate cancer risk in hyperprolactinemia men was reduced (HR 0.40; 95% CI: 0.16-0.99).

CONCLUSIONS

An increased overall cancer risk was found in hyperprolactinemia patients, but no increased risk of breast cancer in women and a reduced risk of prostate cancer in men. These findings warrant further investigations and to be confirmed in larger studies but may indicate the importance of an active treatment strategy and follow-up of hyperprolactinemia patients.

Acute myeloid leukaemia presenting as galactorrhoea

The clinical presentation of acute myeloid leukaemia is variable. We report a 40-year-old woman who presented with a 1-month history of galactorrhoea with an elevated prolactin level. The blood counts were normal, but she was found to have acute myeloid leukaemia with monocytic differentiation. The serum prolactin level normalized after chemotherapy. In the absence of evidence of CNS involvement, the hyperprolactinaemia is presumed to be a paraneoplastic phenomenon. We discuss the potential mechanism of prolactin production in this case.

Gene expression profiling of acute myeloid leukemia with translocation t(8;16)(p11;p13) and MYST3-CREBBP rearrangement reveals a distinctive signature with a specific pattern of HOX gene expression

Acute myeloid leukemia (AML) with translocation t(8;16)(p11;p13) is an infrequent leukemia subtype with characteristic clinicobiological features. This translocation leads to fusion of MYST3 (MOZ) and CREBBP (CBP) genes, probably resulting in a disturbed transcriptional program of a myelomonocytic precursor. Nonetheless, its gene expression profile is unknown. We have analyzed the gene expression profile of 23 AML patients, including three with molecularly confirmed MYST3-CREBBP fusion gene, using oligonucleotide U133A arrays (Affymetrix). MYST3-CREBBP cases clustered together and clearly differentiated from samples with PML-RARalpha, RUNX1-RUNX1T1, and CBFbeta-MYH11 rearrangements. The relative expression of 46 genes, selected according to their differential expression in the high-density array study, was analyzed by low-density arrays in an additional series of 40 patients, which included 7 MYST3-CREBBP AML cases. Thus, genes such as prolactin (PRL) and proto-oncogene RET were confirmed to be specifically overexpressed in MYST3-CREBBP samples whereas genes such as CCND2, STAT5A, and STAT5B were differentially underexpressed in this AML category. Interestingly, MYST3-CREBBP AML exhibited a characteristic pattern of HOX expression, with up-regulation of HOXA9, HOXA10, and cofactor MEIS1 and marked down-regulation of other homeobox genes. This profile, with overexpression of FLT3, HOXA9, MEIS1, AKR7A2, CHD3, and APBA2, partially resembles that of AML with MLL rearrangement. In summary, this study shows the distinctive gene expression profile of MYST3-CREBBP AML, with overexpression of RET and PRL and a specific pattern of HOX gene expression.

Multiple, PKA-dependent and PKA-independent, signals are involved in cAMP-induced PRL expression in the eosinophilic cell line Eol-1

Besides its pivotal role in reproduction, the polypeptide hormone prolactin (PRL) has been attributed an immunomodulatory function. Extrapituitary PRL expression is regulated differently from that in the pituitary, due to the use of an alternative promoter. In leukocytes, cAMP is an important regulator of PRL expression. We report that in the human eosinophilic cell line Eol-1, cAMP-induced PRL expression is partially abrogated by two protein kinase A (PKA) inhibitors (H89, PKI) and by the p38 inhibitor SB203580. Phosphorylation of p38 was PKA-independent and could be stimulated by a methylated cAMP analogue, which specifically activates the exchange factor directly activated by cAMP (EPAC). Furthermore, cAMP induced a PKA-dependent phosphorylation of cAMP-responsive element binding protein (CREB). We postulate that cAMP induces PRL expression via two different signalling pathways: a PKA-dependent pathway leading to the phosphorylation of CREB, and a PKA-independent pathway leading to the phosphorylation of p38.

Regulation of prolactin expression in leukemic cell lines and peripheral blood mononuclear cells

To address the role of different intracellular signals in prolactin (PRL) expression in leukocytes, we have investigated the effects of chlorophenylthio-cAMP (cptcAMP), phorbol myristate acetate (PMA) and ionomycin on the activation of the upstream PRL promoter in several leukemic cell lines. All three stimulators, alone or in synergism with each other, were able to modulate promoter activity, but their actions were cell-type dependent. In freshly isolated peripheral blood mononuclear cells (PBMC), PRL expression could only be stimulated by cptcAMP. The physiological importance of cAMP in the regulation of PRL expression in leukocytes is suggested by the finding that in PBMC, PRL expression is enhanced by prostaglandin-E(2) and the beta(2)-adrenergic agonist terbutaline, which both signal through cAMP.

Prolactin modulates the naive B cell repertoire

Prolactin is a peptide hormone produced by the anterior pituitary gland that is critical in lactation. Prolactin can also be produced by lymphocytes, and both B and T cells express prolactin receptors. These findings have suggested that prolactin has immunomodulatory functions. Studies in spontaneously autoimmune hosts have demonstrated a role for prolactin in augmenting autoreactivity. We chose to analyze prolactin effects on anti-DNA B cells in nonspontaneously autoimmune female BALB/c mice transgenic for the heavy chain of an anti-DNA antibody. Treatment with prolactin for 4 weeks induced a lupus-like phenotype with an increased number of transgene-expressing B cells, elevated serum anti-DNA antibody titers, and glomerular immunoglobulin deposits. Prolactin caused a decrease in the population of transitional B cells and an increase in mature follicular and marginal zone B cells. The DNA-reactive B cells had a follicular cell phenotype. Anti-DNA hybridomas demonstrated that prolactin alters selection of the naive B cell repertoire. The expansion and activation of anti-DNA B cells in prolactin-treated R4A-gamma2b BALB/c mice was dependent on the presence of CD4(+) T cells. Finally, treatment with prolactin was unable to break tolerance in R4A-gamma2b transgenic C57Bl/6 mice, suggesting that responsiveness of the immune system to prolactin is genetically determined.

Prolactin influences proliferation and apoptosis of a human IgE secreting myeloma cell line, U266

In certain types of solid tumours and lymphomas prolactin (PRL) potentiates tumour cell proliferation and exerts anti-apoptotic effect. Tumour cells themselves can produce PRL and express PRL-receptors. Hyperprolactinemia is associated with different tumours, also. Multiple myeloma (MM) is a haematological malignancy caused by the clonal expansion of terminally differentiated plasma cells in the bone marrow. Recently, we demonstrated PRL immunostaining in bone marrow cells of MM patients and an elevated level of serum PRL of MM patients with advanced disease. In the present study, we tested the effect of PRL on a U266 human myeloma cell line and demonstrated constitutive and melphalan-stimulated intracytoplasmic PRL in U266 cells. Exogeneous PRL inhibited the proliferation and immunoglobulin (Ig) production of U266 myeloma cells. Concerning etoposide-induced apoptosis, PRL had a double-faceted effect depending on the applied dose: high, pharmacological doses (corresponding to hyperprolactinemia), inhibited apoptosis, whereas near physiological doses exerted a pro-apoptotic effect. These data indicate a definite effect of PRL on a human myeloma cell line. We demonstrated a direct inhibition of PRL on tumour cell growth, while its reciprocal effect on apoptosis refers to an important regulatory role of PRL.

Prolactin in human systemic lupus erythematosus

In the last decade, evidence has accumulated to support the hypothesis that both mild and moderate elevations of serum prolactin (PRL) participate in the clinical expression and pathogenesis of systemic lupus erythematosus (SLE). Hyperprolactinemia (HPRL) has been found in 20-30% of patients with SLE. HPRL seems to be associated with clinical activity of SLE during pregnancy. Although the relationship between HPRL and active SLE in non-pregnant patients is controversial, recent clinical and experimental studies support the potential role of prolactin (PRL) as a promoter of clinical activity and severity of SLE. Mild elevations of serum PRL secondary to microadenoma could trigger the onset of SLE in a subset of patients. Elevated PRL and interleukin (IL)-6 have been found in the urine of patients with active lupus nephritis and in cerebrospinal fluid (CSF) of patients with active central nervous system (CNS) SLE. PRL may therefore participate in the pathogenesis of lupus nephritis and cerebritis, and the presence of PRL may reflect an abnormal communication between the immune system and the neuroendocrine system in active SLE. Lymphocytes from patients with active SLE produce increased amounts of PRL, and this extrapituitary PRL may participate in aberrant immune processes in SLE. There is exciting new evidence that HPRL in SLE may be explained by stimulation of pituitary PRL secretion by cytokines. In addition, defects in peptidergic modulators and dopamine metabolism have been described in patients with SLE. The interactions between PRL, cytoquines, autoantibodies and organ involvement suggest that PRL participates in local and generalized immune and inflammatory processes and acts as a bridge between the neuroendocrine and immune systems in SLE. Understanding the interactions between these systems in SLE will help us to understand and treat this important autoimmune disease.

Prolactin production by immune cells

Prolactin (PRL) is a pituitary hormone and a cytokine that plays an important role in rodent and human immune responses, including autoimmune diseases. However, many cells and tissues other than the pituitary make PRL, including immune cells. Here, we will present the evidence demonstrating PRL synthesis by different subtypes of immune cells from humans, mice and rats, describe the regulation of PRL gene expression in human lymphocytes, and discuss the functions of PRL made by immune cells. Finally, we will present evidence for involvement of immune cell PRL in human autoimmune disease and suggest how it might play a unique immunoregulatory role.

Growth hormone and prolactin expression in the immune system

Prolactin (PRL) and growth hormone (GH) are pituitary hormones that play pivotal roles in lactation and body growth, respectively. In addition, both hormones have been implicated as modulators of immune responses. Since the expression of GH and PRL by leukocytes points to autocrine or paracrine roles during immune responses, our study is aimed at PRL- and GH-production in leukocytes. We show that human peripheral blood granulocytes, which express GH and PRL mRNA, contain high molecular-weight immunoreactive variants of GH and PRL (37 and 43 kDa, respectively), but not the pituitary-sized hormones. Secretion of these variants, or biologically active material as assessed by the Nb2 bioassay, was not detected. On the other hand, certain leukemic myeloid cells secrete 23-kDa, pituitary-sized, PRL, which is biologically active.

Roles of prolactin and gonadotropin-releasing hormone in rheumatic diseases

PRL is capable of influencing immune responses and is a cytokine in all likelihood. Circulating PRL is elevated in a number of autoimmune diseases, and about 20% of SLE patients are hyperprolactinemic. The serum PRL concentration often does not reflect disease activity in SLE. The PRL-suppressing drug bromocriptine has been reported to benefit small numbers of patients with reactive arthritis and inflammatory eye disease, and bromocriptine may be beneficial in treating SLE. In NZB/NZW mice, bromocriptine was beneficial and prolonged life. Bromocriptine therapy favorably modified disease in human SLE. In a preliminary open-label study, SLE patients treated with bromocriptine for 6 months had significant improvement in disease activity. These responses were corroborated by masted therapeutic studies. Daily treatment with low-dose bromocriptine prevented lupus flares, and bromocriptine was as effective as hydroxychloroquine in treating active nonorgan-threatening disease. The reports of the efficacy of bromocriptine treatment of SLE are encouraging. Additional studies may confirm the findings reported in this review and may lead to further use of hormonal modification to treat lupus and other autoimmune diseases. For the present, it is important to understand that treatment with dopamine agonists such as bromocriptine is experimental and best confined to therapeutic trials. In the experience of the authors, bromocriptine should not be relied on to treat severe life-threatening autoimmune disease. If bromocriptine is used to treat SLE and is then discontinued, the patient should be observed carefully for rebound hyperprolactinemia and the development of a lupus flare. GnRH is produced by lymphocytes and exerts immunomodulatory actions. Thus, GnRH resembles a cytokine. GnRH can be shown to exert gender-restricted immune actions in vitro and in vivo. The authors' preliminary observations are consistent with the possibility that gender-related differences in expression of the GnRH receptor or in GnRH signal transducers may contribute to gender-related differences in immune responsiveness to GnRH. These differences in G proteins may contribute to the gender-related differences in immunity and expression of autoimmune disease.

Myeloid leukemic cells express and secrete bioactive pituitary-sized 23 kDa prolactin

Prolactin (PRL) is a 23 kDa polypeptide hormone of pituitary origin which is of major importance for reproduction. In addition, PRL has immunomodulatory effects and can be produced in small quantities in nonpituitary tissues. To address possible autocrine or paracrine functions of PRL in leukemia, we characterized immunoreactive PRL from the culture medium of leukemic cells. The myeloid cell line Eol-1 expresses the long extrapituitary type mRNA for PRL and synthesizes immunoreactive PRL with a molecular weight of 23 kDa. The biological activity in Eol-1 culture medium was determined using the Nb2 bioassay. This activity co-eluted with recombinant human (rh) PRL on an S-200 Sephacryl gel filtration column and could be blocked by anti-PRL antiserum. Western blot analysis and Nb2 bioassays also suggest that acute myelogenous leukemic blasts secrete bioactive 23 kDa PRL in one out of three tested patients.

Effects of prolactin in stimulating disease activity in systemic lupus erythematosus

Systemic lupus erythematosus (SLE), a chronic autoimmune illness, is influenced by hormones. High prolactin concentrations were associated with early death from autoimmune renal disease in NZB/NZW mice, an animal model of severe SLE. NZB/NZW mice that delivered and nursed pups and those that underwent pseudopregnancy had changes in serum IgG and autoantibodies. NZB/NZW mice treated with the prolactin-suppressing drug bromocriptine had prolonged lives. Elevated serum prolactin concentrations are reported in SLE patients of both sexes. We found four women with long-standing hyper-prolactinemia who developed SLE. A survey of premenopausal women whose sera were submitted for autoantibody testing showed that 20% with anti-ds-DNA antibodies also had high prolactin levels. Many hyperprolactinemic patients whose sera were referred to an endocrinology laboratory had positive FANA tests (women 33%, men 53%) but did not have SLE. Disease activity was suppressed in six of seven SLE patients treated with bromocriptine. All had elevated disease activity and five became unexpectedly hyperprolactinemic after treatment stopped. Manipulating serum prolactin affords a means of treating clinical SLE activity.

Metoclopramide: a novel and safe immunomodulating agent for restoring the depressed macrophage immune function after hemorrhage

BACKGROUND AND OBJECTIVE

Recent studies have shown that administration of the anterior pituitary hormone, prolactin, after hemorrhage restored the depressed immune responses that are observed under those conditions. Because metoclopramide (MCP) is known to increase prolactin secretion and ultimately plasma prolactin levels, we attempted to determine whether administration of metoclopramide after hemorrhage produces any beneficial effects on the depressed splenocyte and peritoneal macrophage immune function after severe hemorrhage.

DESIGN, MATERIALS AND METHODS

Mice were bled to and maintained at a mean arterial pressure of 35 mm Hg for 60 minutes, then adequately resuscitated and segregated into two groups. One group received saline vehicle; animals in the other group were treated with metoclopramide (100 microg/100 g body weight, subcutaneously) before resuscitation. Two hours after saline or MCP injection, the animals were killed and macrophage as well as splenocyte cultures established. Plasma corticosterone levels were also measured.

RESULTS

The proliferative capacity of the splenocytes as well as their ability to release interleukin (IL)-2 and IL-3 in response to mitogen was markedly improved in animals that had hemorrhaged and that were treated with MCP compared with saline-injected mice. Moreover, the depressed splenic and peritoneal macrophage IL-1 and IL-6 release after hemorrhage was restored with MCP treatment. Furthermore, treatment with MCP prevented the increase in blood corticosterone levels seen after severe hemorrhage.

CONCLUSION

These results support the concept that the immunosuppression after hemorrhage may be mediated by hormones from the hypothalamic-pituitary-adrenal axis. Furthermore, MCP may be a useful adjuvant in the treatment of the trauma-hemorrhagic shock-induced immunosuppression.

Endocrine, paracrine and autocrine actions of prolactin on immune cells

The immune response is regulated by locally released factors, collectively referred to as cytokines. Data on the human immune system have convincingly demonstrated that the hormone prolactin (PRL), in addition to exerting its endocrine control on the immune system, acts as a cytokine in that it is released within the immune system and regulates the lymphocyte response by paracrine and autocrine mechanisms. Both lymphocyte and pituitary PRLs are under the control of immune factors. Synthesis of human PRL by lymphocytes is induced by T-cell stimuli, while increased release of PRL by the pituitary, observed in vivo after immune challenge, may be mediated by cytokines produced by monocyte-macrophages. Since hyperprolactinemia and hypoprolactinemia are both immunosuppressive, physiological levels of circulating PRL must be necessary to maintain basal immunocompetence. The effects of Cyclosporin (CsA) on IL-2 and PRL gene activation and the analysis of the intracellular signaling events downstream IL-2 and PRL receptors suggest coordinate actions of these two cytokines during T cell activation.

The immune effects of neuropeptides

Current evidence indicates that the neuroendocrine system is the highest regulator of immune/inflammatory reactions. Prolactin and growth hormone stimulate the production of leukocytes, including lymphocytes, and maintain immunocompetence. The hypothalamus-pituitary-adrenal axis constitutes the most powerful circuit regulating the immune system. The neuropeptides constituting this axis, namely corticotrophin releasing factor, adrenocorticotrophic hormone, alpha-melanocyte stimulating hormone, and beta-endorphin are powerful immunoregulators, which have a direct regulatory effect on lymphoid cells, regulating immune reactions by the stimulation of immunoregulatory hormones (glucocorticoids) and also by acting on the central nervous system which in turn generates immunoregulatory nerve impulses. Peptidergic nerves are major regulators of the inflammatory response. Substance P and calcitonin gene-related peptide are pro-inflammatory mediators and somatostatin is anti-inflammatory. The neuroendocrine regulation of the inflammatory response is of major significance from the point of view of immune homeostasis. Malfunction of this circuit leads to disease and often is life-threatening. The immune system emits signals towards the neuroendocrine system by cytokine mediators which reach significant blood levels (cytokine-hormones) during systemic immune/inflammatory reactions. Interleukin-1, -6, and TNF-alpha are the major cytokine hormones mediating the acute phase response. These cytokines induce profound neuroendocrine and metabolic changes by interacting with the central nervous system and with many other organs and tissues in the body. Corticotrophin releasing factor functions under these conditions as a major co-ordinator of the response and is responsible for activating the ACTH-adrenal axis for regulating fever and for other CNS effects leading to a sympathetic outflow. Increased ACTH secretion leads to glucocorticoid production. alpha-melanocyte stimulating hormone functions under these conditions as a cytokine antagonist and an anti-pyretic hormone. The sympathetic outflow, in conjunction with increased adrenal activity. leads to the elevation of catecholamines in the bloodstream and in tissues. Current evidence suggests that neuroimmune mechanisms are essential in normal physiology, such as tissue turnover, involution, atrophy, intestinal function, and reproduction. Host defence against infection, trauma and shock relies heavily on the neuroimmunoregulatory network. Moreover, abnormalities of neuroimmunoregulation contribute to the aetiology of autoimmune disease, chronic inflammatory disease, immunodeficiency, allergy, and asthma. Finally, neuroimmune mechanisms play an important role in regeneration and healing.

Prolactin increases the susceptibility of primary leukemia cells to NK and LAK effectors

Our previous studies have shown that prolactin (PRL), a pituitary and lymphocyte hormone and a ligand of the cytokine/hemopoietin receptors (R) superfamily, acts synergistically with interleukin (IL)-2 on the development of lymphokine activated killer (LAK) cells and enhances the effects of GM-CSF and IL-3 on myeloid progenitors' proliferation and differentiation. More recently, we have demonstrated that GM-CSF and IL-3 increase the sensitivity of acute myeloid leukemic (AML) cells to LAK activity. Together, these findings have prompted us to study the role of PRL on the target arm of the LAK response. We show here that CD33+ blasts from AML patients express membrane PRL-R and that the PRL/PRL-R interaction is followed by increased susceptibility to natural killer (NK) (p < 0.02) and LAK (p < 0.001) cells. As predicted from the dimerization model of PRL-R and in agreement with previous reports, the response of AML blasts to PRL was bell-shaped with a trend peak at 25 ng/ml. Although enhanced lysis occurred at the target recognition level, it was not accompanied by changes in the MHC class I, cellular adhesion molecules, or myeloid differentiation antigens. Cell cycle recruitment and lysis increased concurrently in three cases studied, suggesting a modulatory action of PRL on the expression of putative cycle-related NK/LAK-target structures. Together, these data strengthen the role of PRL in the LAK response.

Growth hormone and prolactin are paracrine growth and differentiation factors in the haemopoietic system

The pituitary secretory proteins growth hormone (GH) and prolactin (PRL) do not, as yet, have major roles in haematology or immunology. Recent evidence indicates that these hormones are haemopoietic growth factors and exert immunomodulatory functions at physiological concentrations. Here Robert Hooghe and colleagues discuss the significance of these hormones on different aspects of the immune system.

Dopamine-induced lymphoma cell death by inhibition of hormone release

Dopamine inhibits prolactin release from pituitary cells and seems to affect the release of several other hormones as well. We report here that dopamine may have similar effects on human B lymphoma cells leading to inhibition of production or release of endogenous factors required for cell viability and proliferation. Thus, addition of dopamine to serum-free cultures of Burkitt lymphoma cells (Raji, Namalwa, Daudi and Jijoye) resulted in rapid and extensive cell death while a myeloma cell line, SKO, appeared to be refractory to this treatment. The addition of FCS or supernatant from serum-free cultures of Raji or T24 bladder carcinoma cells could, to a variable degree, counteract the effect of dopamine, suggesting that dopamine acts by inhibiting the production of essential autocrine factors. When two of the hormones known to be under dopamine control, i.e. prolactin (PRL) and thyrotropin (TSH), were tested, they were able to prevent dopamine-induced cell death if combined with heparin. We further observed that the reducing agent 2-mercaptoethanol (2-ME), which is known to inhibit the binding of TSH to its receptor, displayed similar effects to those of dopamine and was strongly inhibitory for Burkitt lymphoma but not for myeloma cells. As expected from its blocking activity at the receptor level, the effect of 2-ME could not be reversed by adding exogenous factors. Contrary to its effect on B lymphoma cells, 2-ME is essential for growth of the murine T-cell lymphoma line CTLL. However, we show here that dopamine can fully compensate for 2-ME, suggesting that TSH or another factor under dopamine control is intimately involved in the regulation of T-cell growth. This study lends further support to the notion of an active interplay between the neuroendocrine and immune systems and emphasizes PRL and TSH as important regulators of lymphoid cell function. It also shows that these hormones may contribute to the autonomous growth pattern of B lymphoma cells and suggests a potential role for dopamine in the treatment of B-cell tumours.